A survival analysis of the approval of US patent applications.

We model the length of time that it takes for a patent application to be granted by the US Patent and Trademark Office (USPTO), conditional on the patent actually being awarded eventually. Survival analysis is applied and both the nonparametric Kaplan-Meier and parametric accelerated failure time models are used to analyse the data. We find that the number of claims a patent makes, the number of citations a patent makes, the patent's technological category, and the type of applicant all have significant effects on the duration that a patent is under consideration. A log-normal survival model is the preferred parametric specification, and the results suggest that the hazard function is nonmonotonic over time. [ABSTRACT FROM AUTHOR]